Yup ... simple work around to make WASAPI the exclusive WindoHs! handler is to set the internal OS volume to 100%. Anything else WILL cause all audio to be routed through DirectSound as well, resulting in a somewhat degraded signal, what with additional processing and latency issues.
And also, worth repeating, if your audio server software allows it, set it up for "exclusive access". This locks out anything other that that software (including system sounds) to eliminate conflicts there. One exception there is ASIO drivers - killing some of those can be like killing a vampire - you gots to catch them first, eh. I had a fun fest here trying to get ASIO4All off my machine ... die, driver, DIE!!
Oh. And when it comes to your hardware being able to work with WASAPI, good point there. You'll see a WASAPI source listed in your audio software - if not, sucks to be you ... time to upgrade!